Circuit for adding constant dc bias,supplied by a reference zener diode,to a variable input signal



Sept. 8, 1970 R. H. PARKER 3,528,039

REFERENCE CIRCUIT FOR ADDING CONSTANT DC BIAS SUPPLIED BY A ZENE'RDIODE, TO A VARIABLE INPUT SIGNAL Filed March 22, 1965 i VARIATION 01 0|(D O OI O FIG 3 I5 2 2.5 5 5.5 4 4.5 5 5.5 e 6.5 "I

I INVEVTOR RATIO OF 1 TO I| (-fim) ROBERT H. PARKER ATTORNEYS UnitedStates Patent Ofice Patented Sept. 8., 1970 3,528,039 CIRCUIT FOR ADDINGCONSTANT DC BIAS, SUP- PLIED BY A REFERENCE ZENER DIODE, TO A VARIABLEINPUT SIGNAL Robert H. Parker, Cedar Rapids, Iowa, assignor to CollinsRadio Company, Cedar Rapids, Iowa, :1 corporation of Iowa Filed Mar. 22,1965, Ser. No. 441,550 Int. Cl. H03g 11/00; G011 17/02 US. Cl. 333--14 8Claims ABSTRACT OF THE DISCLOSURE This invention relates to a circuitfor compressing or expanding the percentage of variation or tolerance ofvoltage between nodes of a circuit.

It is frequently desired to increase or lower the percentage ofvariation of the voltage of an AC or DC circuit. This may be desirablein order to permit a more accurate measurement of the voltage variationor else to enable the use of less expensive circuit components asmeasuring equipment. This invention accomplishes both of theseadvantages by adding a known regulated signal to the varying outputsignal to thereby lessen the efiect of the variation of the monitoredsignal.

It is therefore an object of this invention to provide a circuit bywhich the tolerance of an output signal can be compressed or expanded.

It is another object of this invention to provide such a circuit inwhich the tolerance variation can be increased or decreased at will.

It is another object of this invention to provide such a circuit whichis useful with both AC and DC circuits.

Further objects, features, and advantages of the invention will becomeapparent from the following description and claims when read in view ofthe accompanying drawings wherein like numbers indicate like parts andin which:

FIG. 1 shows a tolerance compressor circuit which is useful with DC,

FIG. 2 shows a compressor circuit which is useful with AC,

FIG. 3 shows a graph of percent of variation versus added signal interms of the varying signal.

Referring now to the drawing, FIG. 1 shows four resistors 10, '11, 12,and 13 connected in series. Connected between the junction of resistors10 and 11 and ground is Zener diode 15. A monitoring means 16 isconnected between the junction of resistors 11 and 12 and ground, and avoltage dividing resistor 14 is connected between the junction ofresistors 12 and 13- and ground. If the variation in voltage at theinput V is desired to be compressed or expanded the variation of current1 must also be so compressed or expanded since by proper selection ofcomponent values the variation of I can be essentially equal to thevariation of V The effect of the variation of V and consequently I canbe changed by adding a known regulated signal 1 to I The addition of apositive signal, with respect to 1 causes a compression of tolerance;while the addition of a negative signal increases or expands thetolerance. With Zener diode 15 poled as shown in FIG. 1 a positivecurrent I is added to I by reversing the polarity of the Zener 15 anegative current 1 is added to 1 The effect of the addition of aregulated current, I on the variation of current I can be demonstratedby considering the current I passing through monitor 16. For example, inFIG. 1 the current passing through monitor 16 is I =I -+I i0.25 I (1)Equation -1 shows an assumed 25% variation of 1 for purposes ofillustration; however, any percentage of variation can be compressed orexpanded. The 25 variation is decreased by substituting for current 1 amultiple (A) of current 1 Equation 1 then becomes In this manner thevariation seen by monitor 16 becomes a 10.25 1 variation over a nominalcurrent of I +AI which gives a variation of [0..215ifj1100] (3) Assumingthat it is desired to compress the 25% variation to a 12.5% variationthis can be done by regulating current I such that I :I (i.e. A=1)Substituting this value into Equation 1, the equation then becomes I =2IiO.2-5 1 which in accordance with Equation 3 becomes This is a currentvariation of 10.25 on a nominal current of two which gives a currentvariation of 12.5% as desired. By changing the relationship of I and 1any percentage of variation can be obtained. This is shown in Table 1where A represents the ratio of I to 1 Table I.-I positive A: 1 percentvariation seen by monitor 16 0 25.0

As shown in the table, by allowing the coefficient A to vary from 0.25,which gives a percent variation of p to a value of 7, the percentvariation can be decreased to i3.l3%. It is obvious that the percentvariation can be decreased further simply by increasing the relationshipof 1 to 1 In order to expand the tolerance it is necessary to reversethe polarity of Zener diode 15 and reference voltage VDC as shown inFIG. 1. By doing this the current I is negative with respect to thecurrent I The effect of this is to decrease the value of current asshown in Equation 1. For this reason when the ratio to 1 of I is betweenzero and one (0 A l) the percent of variation changes from a theoreticalinfinite at the value of A-=1 to i 25 at the value of A'=0. For valuesof 1 A 2 tolerance expansion is also accomplished but a reversal ofmonitor 16 polarity is required. For A 2 tolerance compression withmonitor 16 polarity reversal occurs. This is shown in Table 2.

Table II.-I negative A: i% variation seen by monitor 16 Referring now toFIG. 3, the solid curve 22 shows the percent variation versus the Alcurrent relationship for positive values of I and broken curve 23 is asimilar curve for values when I is negative with respect to I FIG. 2shows the circuit of FIG. 1 wherein the circuit is adapted for use withAC inputs. In order to accomplish this, diode 20, resistor 17 andcapacitor 18 are added to the regulated end of the circuit and diode 21and capacitor 19 are added to the monitor end of the circuit. Diode 20is added to rectify the AC signal assuring that only positive values ofcurrent are presented to resistor 17 and capacitor 18 which smooths theinput current. Diode 21 and capacitor 19 perform a similar function onthe monitor end. The operation of the circuit is now the same as that ofthe FIG. 1 circuit. The circuit as shown in FIG. 2 is useful incompressing the variation of voltage V In order to adapt the circuit forexpanding the V tolerance it is necessary to reverse the polarity ofZener diode and diode In the above description both the input current Iand current to be monitored I have been either AC or DC. For example, inFIG. 1 both currents are DC while in FIG. 2 both are AC. The similarityof current forms is not essential to the operation of the invention.FIG. 1 can be modified to add an AC input current I to a DC monitoredcurrent I by adding diode 20, capacitor 17 and resistor 18 t0 the inputend of the circuit in the same manner as shown in FIG. 2. Alternatively,FIG. 1 can be modified to add a DC input current I to an AC monitoredcurrent I by adding capacitor 19 and diode 21 to the monitored end ofthe circuit in the same manner as shown in FIG. 2. It is now evidentthat four combinations are possible.

(1) DC input with DC monitored (2) AC input with AC monitored (3) DCinput with AC monitored (4) AC input with DC monitored Although thisinvention has been described with respect to particular embodimentsthereof, it is not to be so limited, as changes and modifications may bemade therein which are within the spirit and scope of the invention asdefined by the appended claims.

I claim:

1. A monitoring circuit capable of compressing or ex pandin g variationsin a monitored signal comprising monitoring means having first andsecond terminals, first conductive means connected to said first andsecond terminals for receiving an input signal and supplying a firstcurrent to said monitoring means, second conductive means connected tosaid first and second terminals for receiving a reference voltage andsupplying a regulated second current to said monitoring means, saidfirst conductive means comprising a voltage divider means, and saidsecond conductive means comprising a T configuration voltage dividermeans including a shunt connected Zener diode for regulating the secondcurrent through said monitoring means.

2. A monitoring circuit as defined by claim 1 wherein said referencevoltage is a DC voltage, and the polarities of said DC voltage and saidZener diode are arranged so that said first and second currents arecumulative in said monitoring means thereby compressing variations insaid monitored signal.

3. A monitoring circuit as defined by claim 1 wherein said referencevoltage is a DC voltage, and the polarities of said DC voltage and saidZener diode are arranged so that said first and second currents areopposing in said monitoring means thereby expanding variations in saidmonitored signal.

4. A monitoring circuit as defined by claim 1 wherein said secondconductive means further includes a series connected diode and a shuntconnected resistor-capacitor parallel combination for receiving saidreference voltage, said reference voltage being AC.

5. A monitoring circuit as defined by claim 4 wherein the polarities ofsaid shunt diode and said series diode are arranged so that said firstand second currents are cumulative in said monitoring means therebycompressing variations in said monitored circuit.

6. A monitoring circuit as defined by claim 4 wherein the polarities ofsaid shunt diode and said series diode are arranged so that said firstand second currents are opposing in said monitoring means therebyexpanding variations in said monitored circuit.

7. A monitoring circuit as defined by claim 1 wherein said firstconductive means includes a series connected diode and a shunt capacitorfor receiving said input signal, said input signal being AC.

8. A monitoring circuit as defined by claim 4 wherein said firstconductive means includes a series connected diode and a shunt capacitorfor receiving said input signal, said input signal being AC.

References Cited UNITED STATES PATENTS 2,533,769 12/1950 Couillard324-131 2,874,354 2/1959' Bell 324-431 OTHER REFERENCES The Zener Diode,Shaughnessy; Popular Electronics, June 1961, pp. 76-82.

ELI LIEBERMAN, Primary Examiner M. NUSSBAUM, Assistant Examiner U.S. Cl.X.R. 324-98

